The purpose of this project is to develop pharmacokinetic models and methods for quantitating the mechanisms of the uptake, distribution, metabolism, and excretion kinetics of environmental xenobiotics in various animal species. Mathematical models of the in vivo pharmacokinetics of several halogenated biphenyls in the rat have been developed and have been scaled to the mouse. Other models have been constructed to describe the disposition of these environmental contaminants in animals following chronic exposure. The pharmacokinetics of xenobiotics in marine animals that serve as human food sources is also being modeled. These mathematical models are intended to provide functional strategies for helping to extrapolate the disposition of chemical contaminants in the environment from one compound to another, and from one animal species to another, ultimately to include man. The evaluation and implementation of existing techniques and the development of new methodologies needed to accomplish these objectives are an integral part of this project.